The invention relates to a fluidic switch for apparatus for measurement, regulation or control, which is comprised of the following: a switch housing consisting of two halves; two actuating chambers within the housing, into which chambers the actuating passages lead, the said chambers being separated by an actuating membrane having at its circumferential margin a sealing bolster substantially parallel to the plane of separation of the housing halves; a switch valve chamber having fluid inlets and outlets; and an actuating lever extending from the actuating membrane into the switch valve chamber, constructed as a plate valve body at the end of the membrane which extends into said switch valve chamber, and fulcrumed about an axis parallel to the plane of separation on a fulcrum bushing in the form of a resilient elastomeric crosspiece made integrally with the actuating lever and separating the actuating chamber from the switch valve chamber, the said crosspiece being clamped within internal transverse grooves provided in the housing halves parallel to the plane of separation.
Such switches, as they have become known through German "Auslegeschrift" 1,303,304, are required in large numbers for apparatus and systems for the performance of logic operations and elementary circuits, for example, it being fundamentally possible, of course, to use liquids and other fluids instead of compressed air as the controlling medium. For the application described above, switches of the kind in question must be of particularly simple construction and inexpensive to produce in mass production. In addition, the switches, for reasons of miniaturization, must occupy little space, must be east to install and remove, and nevertheless must be reliable in operation. Miniaturization is especially important in the production of pneumatic or hydraulic switching, controlling or regulating apparatus by means of bearing rails and conduit systems, such as those described in German Pat. No. 1,917,727, German "Offenlegungsschrift" 2,018,928, or German "Offenlegungsschrift" 2,146,041, which are hereby cited in full in this regard.
In the known switch described above, as it is described in German Auslegeschrift 1,303,304 or 1,301,724, and which has basically proven to be excellent, the actuating membrane is substantially circular in shape and is surrounded by an annular sealing bolster which, as a result of its compression between the two halves of the housing by means of appropriate fastening means, seals the two actuating chambers not only from one another but also from the outside. The actuating lever is embedded approximately centrally in the actuating membrane and from the edge of the embedded surface which stiffens the middle of the membrane, it departs from the plane of the membrane, and the sloping section of the lever leading away from the actuating membrane is adjoined by a long section parallel to the plane of separation, which outside of the annular sealing bolster surrounding the actuating membrane passes through a lead-through bushing consisting, like the membrane, of rubber or rubber-like material, the plate-like valve body being in turn disposed on the end of the actuating lever farthest from the actuating membrane, at a distance from the lead-through bushing, and being able, according to the pressure in the actuating chambers separated by the membrane, to be brought into engagement with the valve openings of two confronting fluid outlet passages, thereby providing a communication between either of the fluid passages and a central switching valve chamber.
Whereas in the known switch the sealing of the two actuating chambers from one another and from the outside by the annular sealing bolster is entirely satisfactory, the seal between the two actuating chambers on the one hand and the switching valve chamber containing the valve body at the end of the actuating lever on the other hand presents difficulties, inasmuch as the lead-through bushing is under constant compression producing sealing action only perpendicularly to the plane of separation of the housing, not in the direction of the fulcrum of the actuating lever, so that the danger exists that either control fluid or hydraulic pressure fluid leak laterally around the lead-through bushing. This results, in a highly undesirable manner, in interactions between the hydraulic pressure fluid and the control fluid system, which can greatly diminish the reliability of operation of the switch. Furthermore, it has been found that, due to the need for the spatial separation of the actuating membrane, the sealing bolster and the lead-through bushing, the known switch still is not small enough for a great number of applications.